Heat dissipation material and light emitting diode package including a junction part made of the heat dissipation material

ABSTRACT

Disclosed are a heat dissipation material comprising a metallic glass and an organic vehicle and a light emitting diode package including at least one of a junction part, wherein the junction part includes a heat dissipation material including a metallic glass.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.13/213,730, filed on Aug. 19, 2011, which claims priority to and thebenefit of Korean Patent Application No. 10-2010-0081007 filed in theKorean Intellectual Property Office on Aug. 20, 2010, the entirecontents of each of which is incorporated herein by reference.

BACKGROUND

1. Field

This disclosure relates to a heat dissipation material and a lightemitting diode package including a junction part made of the heatdissipation material.

2. Description of the Related Art

A light emitting diode is a diode that emits light when current flows,and it is applied to a variety of electronic devices. In the lightemitting diode, when a forward voltage is applied to a semiconductormaterial, electrons and holes are transferred and combined through a PNjunction, and the energy generated from the combination of electrons andholes is emitted in the form of light and heat. To emit high luminanceand high efficiency light, a portion of the energy lost by heat may bereduced and a portion emitted in the form of light may be increased. Thelight emitting diode may have increased photoefficiency and improvedlifespan by reducing thermal loss. The thermal loss is mainly related toa junction point of a light emitting diode.

SUMMARY

An exemplary embodiment of this disclosure provides a heat dissipationmaterial that may improve heat dissipation characteristics.

Another embodiment of this disclosure provides a light emitting diodepackage including a junction part formed of the heat dissipationmaterial.

According to one aspect of this disclosure, a heat dissipation materialincluding a metallic glass and an organic vehicle is provided.

The metallic glass may have a supercooled liquid region.

The supercooled liquid region may be a temperature region between aglass transition temperature and a crystallization temperature of themetallic glass, and the metallic glass may have a liquid-like behaviorin the supercooled liquid region.

The metallic glass may have a supercooled liquid region ranging fromabout 5° C. to about 200° C.

The metallic glass may have a glass transition temperature of about 150°C. to 500° C.

The metallic glass may include an alloy including at least one ofaluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), zirconium (Zr),iron (Fe), magnesium (Mg), calcium (Ca), cobalt (Co), palladium (Pd),platinum (Pt), gold (Au), cerium (Ce), lanthanum (La), yttrium (Y),gadolinium (Gd), beryllium (Be), tantalum (Ta), gallium (Ga), hafnium(Hf), niobium (Nb), lead (Pb), platinum (Pt), silver (Ag), phosphorus(P), boron (B), silicon (Si), carbon (C), tin (Sn), molybdenum (Mo),tungsten (W), manganese (Mn), erbium (Er), chromium (Cr), praseodymium(Pr), thulium (Tm), or a combination thereof.

The metallic glass may include an alloy including at least one ofaluminum (Al), copper (Cu), or a combination thereof.

The heat dissipation material may further include a thermal conductiveparticle.

The thermal conductive particle may include at least one of aluminum(Al), copper (Cu), titanium (Ti), nickel (Ni), zirconium (Zr), iron(Fe), magnesium (Mg), calcium (Ca), cobalt (Co), palladium (Pd),platinum (Pt), gold (Au), cerium (Ce), lanthanum (La), yttrium (Y),gadolinium (Gd), beryllium (Be), tantalum (Ta), gallium (Ga), hafnium(Hf), niobium (Nb), lead (Pb), platinum (Pt), silver (Ag), phosphorus(P), boron (B), silicon (Si), carbon (C), tin (Sn), molybdenum (Mo),tungsten (W), manganese (Mn), erbium (Er), chromium (Cr), praseodymium(Pr), thulium (Tm), or a combination thereof.

The thermal conductive particle may include at least one of aluminum(Al), copper (Cu), silver (Ag), tin (Sn), or a combination thereof.

According to another aspect of this disclosure, a light emitting diodepackage includes at least one of a junction part, wherein the junctionpart may be included a heat dissipation material including a metallicglass.

The light emitting diode package may further include light emittingdiode chip; a metal wire electrically connected to the light emittingdiode chip; and a printed circuit board electrically connected to themetal wire, wherein the junction part may include a first junction partdisposed between the light emitting diode chip and the metal wire, and asecond junction part disposed between the metal wire and the printedcircuit board.

The light emitting diode package may further include a heat dissipatingplate disposed under the printed circuit board, and the junction partmay further include a third junction part disposed between the printedcircuit board and the heat dissipating plate.

The heat dissipation material may further include a thermal conductiveparticle.

The thermal conductive particle may include at least one of aluminum(Al), copper (Cu), titanium (Ti), nickel (Ni), zirconium (Zr), iron(Fe), magnesium (Mg), calcium (Ca), cobalt (Co), palladium (Pd),platinum (Pt), gold (Au), cerium (Ce), lanthanum (La), yttrium (Y),gadolinium (Gd), beryllium (Be), tantalum (Ta), gallium (Ga), hafnium(Hf), niobium (Nb), lead (Pb), platinum (Pt), silver (Ag), phosphorus(P), boron (B), silicon (Si), carbon (C), tin (Sn), molybdenum (Mo),tungsten (W), manganese (Mn), erbium (Er), chromium (Cr), praseodymium(Pr), thulium (Tm), or a combination thereof.

The thermal conductive particle may include at least one of aluminum(Al), copper (Cu), silver (Ag), tin (Sn), or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view showing a light emitting diode packageaccording to one embodiment.

DETAILED DESCRIPTION

Exemplary embodiments will hereinafter be described in further detailwith reference to the accompanying drawings, in which variousembodiments are shown. This disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to the exemplaryembodiments set forth herein.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. It will be understood that,although the terms “first,” “second,” “third” etc. may be used herein todescribe various elements, components, regions, layers, and/or sections,these elements, components, regions, layers, and/or sections should notbe limited by these terms. These terms are only used to distinguish oneelement, component, region, layer, or section from another element,component, region, layer, or section. Thus, “a first element,”“component,” “region,” “layer,” or “section” discussed below could betermed a second element, component, region, layer, or section withoutdeparting from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising,” or“includes” and/or “including” when used in this specification, specifythe presence of stated features, regions, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, regions, integers, steps,operations, elements, components, and/or groups thereof. The term “atleast one” means a combination comprising one or more of the listedcomponents may be used.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

Hereafter, the term “element” refers to a metal and a semimetal.

First, a heat dissipation material according to one embodiment of thisdisclosure is described.

The heat dissipation material according to one embodiment includes ametallic glass and an organic vehicle.

The metallic glass includes an alloy having a disordered atomicstructure including two or more elements. The metallic glass may be anamorphous metal. The metallic glass may have about 50 to about 100weight percent (“wt %”), specifically about 70 to about 100 wt %, morespecifically about 90 to about 100 wt % amorphous content, based on atotal weight of the metallic glass. Because the metallic glass has a lowresistivity, and thus is different from an insulating glass such as asilicate, it may be considered to be an electrical conductor.

The metallic glass has a supercooled liquid region (ΔTx). Thesupercooled liquid region (ΔTx) is a region between a glass transitiontemperature (Tg) and a crystallization temperature (Tc) of metallicglass. In the supercooled liquid region, a metallic glass has relativelylow viscosity and goes through plastic deformation and shows aliquid-like behavior.

The supercooled liquid region (ΔTx) of metallic glass ranges from about5° C. to about 200° C. Within the range, the supercooled liquid region(ΔTx) of the metallic glass may range from about 5° C. to about 100° C.In the supercooled liquid region (ΔTx), the metallic glass has aliquid-like behavior and it may form a junction point with respect to alower layer and an upper layer.

Meanwhile, the metallic glass may have glass transition temperature(Tg), the starting temperature of the supercooled liquid region (ΔTx),of about 150° C. to about 500° C. By having a glass transitiontemperature of about 150° C. to about 500° C., a relatively lowtemperature, the metallic glass may be applied as a junction point to alight emitting diode package, as mentioned later.

The metallic glass may have an equivalent thermal conductivity, comparedto a conventional metal solder, such as a Au—Sn solder or a Sn—Ag—Cusolder. Accordingly, the heat dissipation material including themetallic glass may be applied as a junction point between the lowerlayer and the upper layer.

The metallic glass may include an alloy including at least one ofaluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), zirconium (Zr),iron (Fe), magnesium (Mg), calcium (Ca), cobalt (Co), palladium (Pd),platinum (Pt), gold (Au), cerium (Ce), lanthanum (La), yttrium (Y),gadolinium (Gd), beryllium (Be), tantalum (Ta), gallium (Ga), hafnium(Hf), niobium (Nb), lead (Pb), platinum (Pt), silver (Ag), phosphorus(P), boron (B), silicon (Si), carbon (C), tin (Sn), molybdenum (Mo),tungsten (W), manganese (Mn), erbium (Er), chromium (Cr), praseodymium(Pr), thulium (Tm), or a combination thereof.

In one embodiment, the metallic glass may include an alloy including atleast one of aluminum (Al), copper (Cu), or a combination thereof, andin another embodiment, the metallic glass may include an alloy includingaluminum (Al) or an aluminum-copper (Al—Cu) alloy.

The following Table 1 shows examples of alloys including aluminum (Al).

TABLE 1 Glass transition Crystallization Supercooled liquid temperaturetemperature region (Tg, ° C.) (Tc, ° C.) (ΔTx) Al_(85.35)Y₈Fe₆V_(0.65)285 365 80 Al₈₅Y₈Fe₆V_(0.65)O_(0.35) 285 355 70 Al_(84.35)Y₈Fe₆V0_(.65)O285 355 70 Al_(87.5)Y₇Fe₅V_(0.5) 280 340 60 Al_(87.5)Y₇Fe₅Ti_(0.5) 275310 35 Al₈₇Y₇Fe₅Ti 270 340 70 Al₈₆Y₇Fe₅Ti₂ 280 350 70 Al₈₈Y₇Fe₅ 258 28022 Al₈₄Ni₁₀Ce₆ 273 286 13 Al₈₈Ni₄Sm₈ 220 241 21 Al₈₅Y₈Ni₅Co₂ 267 297 30Al₈₅Gd₈Ni₅Co₂ 281 302 21 Al₈₅Dy₈Ni₅Co₂ 277 303 26 Al₈₅Er₈Ni₅Co₂ 274 30531 Al₈₅Ni₁₀Ce₅ 246 264 18 Al₈₄La₆Ni₁₀ 273 289 16

The metallic glass may be formed according to known methods such as amelt spinning method, an infiltration casting method, a gas atomizationmethod, an ion irradiation method, or a mechanical alloying method.

The organic vehicle may include an organic compound, an optional organicsolvent, and optional additives known for use in the manufacture of heatdissipation materials for electronic devices. The organic vehicle iscombined with the metallic glass primarily to provide a viscosity andrheology to the heat dissipation material effective for printing orcoating the heat dissipation material. A wide variety of inert organicmaterials can be used, and can be selected by one of ordinary skill inthe art without undue experimentation to achieve the desired viscosityand rheology, as well as other properties such as dispersibility of themetallic glass, stability of the metallic glass and any dispersionthereof, drying rate, firing properties, and the like. Similarly, therelative amounts of the organic compound, any optional organic solvent,and any optional additive can be adjusted by one of ordinary skill inthe art without undue experimentation in order to achieve the desiredproperties of the heat dissipation material.

The organic compound may be a polymer, for example, at least oneselected from a C1 to C4 alkyl (meth)acrylate-based resin; a cellulosesuch as ethyl cellulose or hydroxyethyl cellulose; a phenolic resin;wood rosin; an alcohol resin; a halogenated polyolefin such astetrafluoroethylene (e.g., TEFLON); and the monobutyl ether of ethyleneglycol monoacetate.

The organic vehicle may further optionally include at least one additiveselected from, for example, a surfactant, a thickener, and a stabilizer.

The solvent may be any solvent capable of dissolving or suspending theabove other components of the heat dissipation material and may be, forexample, at least one selected from terpineol, butylcarbitol,butylcarbitol acetate, pentanediol, dipentyne, limonene, anethyleneglycol alkylether, a diethyleneglycol alkylether, anethyleneglycol alkylether acetate, a diethyleneglycol alkyletheracetate, a diethyleneglycol dialkylether acetate, a triethyleneglycolalkylether acetate, a triethylene glycol alkylether, a propyleneglycolalkylether, propyleneglycol phenylether, a dipropyleneglycol alkylether,a tripropyleneglycol alkylether, a propyleneglycol alkylether acetate, adipropyleneglycol alkylether acetate, a tripropyleneglycol alkyl etheracetate, dimethylphthalic acid, diethylphthalic acid, dibutylphthalicacid, and desalted water.

The metallic glass and the organic vehicle may be included at about 0.1to about 99.9 wt % and about 0.1 to about 99.9 wt % based on the totalamount of the heat dissipation material, respectively.

Meanwhile, the heat dissipation material may further include a thermalconductive particle. The thermal conductive particle may be selectedfrom metals having a relatively high thermal conductivity. The thermalconductive particle may include at least one of aluminum (Al), copper(Cu), titanium (Ti), nickel (Ni), zirconium (Zr), iron (Fe), magnesium(Mg), calcium (Ca), cobalt (Co), palladium (Pd), platinum (Pt), gold(Au), cerium (Ce), lanthanum (La), yttrium (Y), gadolinium (Gd),beryllium (Be), tantalum (Ta), gallium (Ga), hafnium (Hf), niobium (Nb),lead (Pb), platinum (Pt), silver (Ag), phosphorus (P), boron (B),silicon (Si), carbon (C), tin (Sn), molybdenum (Mo), tungsten (W),manganese (Mn), erbium (Er), chromium (Cr), praseodymium (Pr), thulium(Tm), or a combination thereof.

In one embodiment, the thermal conductive particle may be at least oneof aluminum (Al), copper (Cu), silver (Ag), tin (Sn), or a combinationthereof.

The thermal conductive particle may have a size (e.g., average largestparticle size) ranging from about 1 nanometers (nm) to about 50micrometers (μm), specifically about 0.1 μm to about 40 μm, specificallyabout 0.5 μm to about 40 μm, more specifically about 1 μm to about 30μm. The thermal conductive particle may be irregular, or have aspherical, rod-like, or plate-like shape.

The thermal conductive particle may improve a thermal conductivity ofthe heat dissipation material.

When the thermal conductive particle is included, the metallic glass,the thermal conductive particle and the organic vehicle may be includedat about 0.1 wt % to about 99.8 wt %, about 0.1 wt % to about 99.8 wt %and about 0.1 to 99.8 wt % based on the total amount of the heatdissipation material, respectively.

The above-described heat dissipation material may be prepared in theform of a paste and applied to a portion of an electronic device in needof the heat dissipation characteristic through a method such as screenprinting or dispensing.

The heat dissipation material may be applied to a junction part of alight emitting diode package among its application fields.

Hereafter, a light emitting diode package adopting the above-describedheat dissipation material is described by referring to the accompanyingdrawings.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

Referring FIG. 1, a light emitting diode package according to oneembodiment is described.

FIG. 1 is a cross-sectional view showing a light emitting diode packageaccording to one embodiment.

The light emitting diode package includes a light emitting diode chip50, a metal wire 40 connected to a light emitting diode chip 50 througha bonding wire 33 and extended to an outer terminal, a mold 30 housingthe light emitting diode chip 50 and fixing the metal wire 40, a printedcircuit board 20 disposed under the mold 30, and a heat dissipatingplate (heat sink) 10 disposed under the printed circuit board 20.

Meanwhile, the light emitting diode package further includes a firstjunction part 35 that is disposed between the light emitting diode chip50 and the metal wire 40 and forming a junction point between them as ajunction part, and a second junction part 25 disposed between the metalwire 40 and the printed circuit board 20 and forming a junction pointbetween them as a junction part. Also, the light emitting diode packagefurther includes a third junction part 15 disposed between the printedcircuit board 20 and the heat dissipating plate 10 and forming ajunction point between them.

The first to third junction parts are directly related to the heatdissipation of the light emitting diode. When the light emitting diodeoperates, the energy provided to the light emitting diode may betransferred as a form of light and/or heat. If the temperature of thejunction parts of the light emitting diode is decreased, the amount ofheat generated from the light emitting diode may decrease and the amountof light emitted from the light emitting diode may increase. Further, itis possible to prevent the light emitting diode from being deterioratedby heat, thus the life-span of the light emitting diode may be improved.For example, when the temperature of the junction part is decreased byabout 11° C., the amount of generated heat is decreased and thereby theamount of emitted light of the light emitting diode may be increased andthe lifespan may be improved to more than double.

To decrease the temperature of the first to third junction parts, thefirst junction part 35, the second junction part 25, and/or the thirdjunction part 15 may include a metallic glass and be formed using theaforementioned heat dissipation material including the metallic glass.The aforementioned heat dissipation material including a metallic glassmay replace a conventional metal solder such as a Au—Sn solder or aSn—Ag—Cu solder.

As described above, the metallic glass has a supercooled liquid region(ΔTx) where the metallic glass may have a liquid-like behavior and showplastic deformation. Accordingly, a junction point may be formed betweena lower layer and an upper layer by reflowing the aforementioned heatdissipation material including the metallic glass, instead of theconventional metal solder. Referring to FIG. 1, the first junction part35 may form a junction point between the light emitting diode chip 50and the metal wire 40, while the second junction part 25 may form ajunction point between the metal wire 40 and the printed circuit board20.

Herein, as described above, since the glass transition temperature (Tg)of the metallic glass is about 150° C. to 500° C., the junction pointsmay be formed at a relatively low temperature compared to aconventional, metal solder, and thus is advantageous in terms ofprocessing time and cost.

In addition, since the metallic glass has an equivalent thermalconductivity compared to a conventional metal solder, it may have asufficient heat dissipation characteristic.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A light emitting diode package comprising: atleast one junction part within the light emitting diode package, whereinthe junction part comprises a heat dissipation material comprising ametallic glass, wherein the metallic glass is an alloy having adisordered atomic structure including two or more metals and has asupercooled liquid region that is a temperature region between a glasstransition temperature and a crystallization temperature of the metallicglass, and the metallic glass has a liquid-like behavior in thesupercooled liquid region, the alloy being a homogenous compound wherethe two or more metals are atomically bonded together.
 2. The lightemitting diode package of claim 1, further comprising: a light emittingdiode chip; a metal wire electrically connected to the light emittingdiode chip; and a printed circuit board electrically connected to themetal wire, wherein the junction part comprises: a first junction partdisposed between the light emitting diode chip and the metal wire; and asecond junction part disposed between the metal wire and the printedcircuit board.
 3. The light emitting diode package of claim 2, furthercomprising a heat dissipating plate disposed under the printed circuitboard, wherein the junction part further comprises: a third junctionpart disposed between the printed circuit board and the heat dissipatingplate.
 4. The light emitting diode package of claim 1, wherein the heatdissipation material further comprises a thermal conductive particle. 5.The light emitting diode package of claim 4, wherein the thermalconductive particle comprises at least one of aluminum (Al), copper(Cu), titanium (Ti), nickel (Ni), zirconium (Zr), iron (Fe), magnesium(Mg), calcium (Ca), cobalt (Co), palladium (Pd), platinum (Pt), gold(Au), cerium (Ce), lanthanum (La), yttrium (Y), gadolinium (Gd),beryllium (Be), tantalum (Ta), gallium (Ga), hafnium (Hf), niobium (Nb),lead (Pb), platinum (Pt), silver (Ag), phosphorus (P), boron (B),silicon (Si), carbon (C), tin (Sn), molybdenum (Mo), tungsten (W),manganese (Mn), erbium (Er), chromium (Cr), praseodymium (Pr), thulium(Tm) , or a combination thereof.
 6. The light emitting diode package ofclaim 5, wherein the thermal conductive particle comprises at least oneof aluminum (Al), copper (Cu), silver (Ag), tin (Sn), or a combinationthereof.
 7. The light emitting diode package of claim 1, wherein themetallic glass has a supercooled liquid region ranging from about 5° C.to about 200° C.
 8. The light emitting diode package of claim 1, whereinthe metallic glass has a glass transition temperature of about 150° C.to 500° C.
 9. The light emitting diode package of claim 1, wherein themetallic glass includes at least one of aluminum (Al), copper (Cu),titanium (Ti), nickel (Ni), zirconium (Zr), iron (Fe), magnesium (Mg),calcium (Ca), cobalt (Co), palladium (Pd), platinum (Pt), gold (Au),cerium (Ce), lanthanum (La), yttrium (Y), gadolinium (Gd), beryllium(Be), tantalum (Ta), gallium (Ga), hafnium (Hf), niobium (Nb), lead(Pb), platinum (Pt), silver (Ag), phosphorus (P), boron (B), silicon(Si), carbon (C), tin (Sn), molybdenum (Mo), tungsten (W), manganese(Mn), erbium (Er), chromium (Cr), praseodymium (Pr), thulium (Tm), or acombination thereof.
 10. The light emitting diode package of claim 9,wherein the metallic glass alloy includes at least one of aluminum (Al),copper (Cu), or a combination thereof.
 11. The light emitting diodepackage of claim 1, wherein the heat dissipation material furthercomprises an organic vehicle.
 12. The light emitting diode package ofclaim 6, wherein the thermal conductive particle comprises at least twoof aluminum (Al), copper (Cu), silver (Ag) and tin (Sn).
 13. The lightemitting diode package of claim 7, wherein the metallic glass has aglass transition temperature of about 150° C. to 500° C.
 14. The lightemitting diode package of claim 10, wherein the metallic glass alloyincludes aluminum (Al) and copper (Cu).
 15. The light emitting diodepackage of claim 1, wherein the junction part includes, at least one ofa first junction part disposed between a light emitting diode chip and ametal wire, a second junction part disposed between a metal wire and aprinted circuit board, and a third junction part disposed between aprinted circuit board and a heat dissipating plate.